I recommend checking out the Denver Mattress Rest Easy Plush RV Bunk Bed Mattress - 72" Long x 30" Wide # DE99ZR for a standard mattress. This is more of a mid-level foam mattress so you aren't getting bad quality or a high price tag. I don't have the dimensions of what mattresses fit your toy hauler so you'll want to double check that as well.
It's also very important to make sure you have those mice taken care of if you haven't already as there isn't a way to mouse-proof any mattress... view full answer...